Magnetron device



Oct. 15, 1957 P. H. PETERS, JR., EIAL 2,810,095

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United. States Patent 2,810,095 MAGNETRON DEVICE Philip H. Peters, Jr.,:Schenectady, and -Dl1iltlA. Wilbur,

Albany, N. Y assignors.-t0;General Electric'Conipany, a corporation of New York The present invention relates to improved magnetron devices which are "particularly suited for anode voltage tuning.

In our copending application, Serial No. 169,712, filed June 22, 1950, entitled Magnetron and Systems Therefor, now Patent No. 2,774,039 and assigned to the same assignee as this application, we described and claimed a method and apparatus for tuning a magnetron system over a substantial frequency range by varying the anode voltage. As outlined in that application, we have found that the oscillating frequency of a magnetron will vary directly with the direct current voltage applied to the anode-cathode circuit if the rate of increase of the high frequency voltage with respect to an increase in the direct current anode-cathode voltage is properly controlled. We have further found thatthe variation of the high frequency voltage with direct current anode-cathode 'the anode circuit is heavily and uniformly loaded over the entire tuning range and at the same time the number of electrons in the interaction space is suitably limited. The present invention provides a magnetron structure having electrical characteristics which are compatible with these requirements for voltage tuning.

In addition, the structure is simple, sturdy, relatively easy to reproduce with accuracy and capable of dissipating large amounts of heat for the physical size of the device involved. The invention, therefore, contemplates improved magnetron devices which are not limited in their use to voltage-tuned applications and which are well suited to quantity manufacture for very high frequency applications or for larger power, lower frequency applications.

It is an object of our invention to provide a new and improved magnetron construction.

It is another object of our invention'to provide an improved cathode assembly for a magnetron device.

It is a still further object of our invention to provide an improved magnetron construction which is particularly suited to either voltage or tank tuning applications.

Further objects and advantages of our invention will become apparent as the following description proceeds, reference being had to the accompanying drawing and its scope will be pointed out in the appended claims. In the drawing, Fig. 1 is an elevational view in section of a magnetron device embodying our invention, the planes of the section being shown by the line 11 of Fig. 2, and Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1.

Referring now to the drawing, we have shown a specific magnetron device embodying the features of our invention. The envelope of the device is made up of a stack of alternately arranged metal and ceramic members, the metal members forming the terminals of the device and the ceramic members forming the insulating spacers therefor. As shown in the drawing, the terminal members include a pair of annular anode terminals and '11 spaced by a ceramic cylinder 12. The envelope is 2 completed .by a pair of disc-shaped metal members 13 and 14 which are spaced from the anode terminals by cylindrical ceramic insulators 15 and 16. The" cathode is supported axially of thecylindrical envelope by means .of integrally formed cylindrical posts 17 and 18 extending inwardly from the terminals 13 and 14 and terminating in spaced relation. The post 18 is provided with an end portion 19 of reduced diameter with respect to the post 18 but with a diameter equal to that of the post '17. The cathode is completed by a spiral 20 which may to advantage be formed of thoriated tungsten. The spiral has an inner diameter substantially equal to the post 17 and the end portion 19 so that it engages the surface of these supporting'portions snugly. Since in the preferred embodiment the cathode terminals 13 .and 14 are .formed of a relatively good conductor, such as copper, and the helix 20 is of thoriated tungsten, the fit between these parts'may be made snug and the tungsten will tend to form a slight groove in the copper when the cathode is assembled. Also since the copper expands more with temperature than the tungsten, the fit Fbecomes tighter "as the tuhefis raised to operating temperatures. In this way, no brazing or similar fastening operation is required between the parts of the cathode assembly in order to insure an adequate electrical and mechanical connection during operation of the device.

The magnetron device illustrated is of.the interdigital 'type and the anode assembly includes two sets of axially extending segments alternately arranged in a cylindrical array about the.cathode. Alternate segments 21 and 22 are connected to a dilferent one of the annular anode terminals "10 and 11 'so'that we have two groups ofanode segments, alternately arranged in the array and with each groupconnected to one of the terminals. The segments are slightly spaced to provide axially extending interaction gaps facing the space charge region between the .anode and cathode. 'The anode segments are coextensive -in.axial length, or, in other words, the free ends of one set of segments terminate in the same plane as the fixed ends'of the remaining set of segments. This reduces the coupling that would exist between the cathode and anodeif the axial overlap of the segments of the two sets were less than Indexing notches 24 are suitably located in the terminals 10 and 11 so that they are in alignment when the anode segments of the two groups are properly spaced circumferentially. In assembly, the terminals 10 and 11 are held in the desired position byasuitable key engaging the positioning notches 24. As indicated earlier, it is desirable that the emission in the space charge path between the. anode and cathode be limited in order to establish the conditions best suited to voltage tuning. The total emission from the cathode is established, in .the absence of ,excessiveback heating, bythefilamentcurrent. In addition, the cathode assembly isdesigned tobring about an inherent emission-limited condition within'the anode-cathode space. The active emitting portion of the cathode is rather small and it is located partially outside of the interaction space. From the drawing, it will be apparent that only the portion of the helix between the spaced ends of cathode supports 17 and 18 is effective since the end turns are-electrically short circuited and also-cooledby the relatively massive "supports. Of the effective length, only about one-half thereof is located within the interaction space. By being olfset in this manner, a smaller proportion of the avail- "able emission is eifective in generating oscillations than would be. the case if the emitter were located'entirely within the interaction space. While complete removal of the emitter from beneath the anodes results in the most compromise between the magnitude of the high frequency power and the uniformity of this power over the tuning range.

The portion of the cathode helix within the array of anode segments is subject to back heating by returning electrons. If no design precautions are taken, this back heating can produce a continuing increase in the number of electrons and provide a regenerative change in high frequency power with changes in anode voltage or anode circuit loading. This condition is incompatible with voltage tuning. It is apparent that, for any particular application of the tube for voltage tuning, the amount of the, cathode exposed to the fields existing between the anode-cathode space and as a result subject to back heating may be determined simply by the positioning of the portion of the cathode helix which is between the supports with respect to the anode structure. In terms of structure, all that is necessary is to change the lengths of the cathode supporting posts 17 and 18. While, as illustrated, the active part of the cathode helix extends about half way into the anode-cathode space, it is contemplated that the entire cathode emitter may be positioned beyond a plane passing through one end of the anode assembly. Preferably, the diameter of the outside of the cathode helix is equal to the diameter of the larger portion 18 of the cathode support so that with respect to the anode-cathode voltage the fields produced in the anode-cathode region are substantially uniform. The post 19 absorbs the heat produced by returning electrons without producing secondary emission. The mass of the post 19 and its connection with disc 14 help to cool it.

The magnetron device described above may to advantage be evacuated and the parts forming the envelope thereof bonded together in a single operation. For example, the ends of the ceramic cylinders may be coated with titanium hydride and the parts arranged in a stack and suitably held together by a clamp which includes a key for engaging the notches 24 and thereby positions the anode segments. The assembly may then be placed in a bell jar (not shown) and evacuated. Within the bell jar there is also a solder pot containing a suitable solder, such as lead. Means for heating the discharge device and solder pot may include a cylindrical oven of suitable metal, such as tantalum. The oven is raised to a suitable temperature, such as 800 C., by induction heating and the tube degassed and evacuated. The solder pot is then elevated or the tube lowered to immerse a part of the tube (which is supported with its axis horizontal) into the molten solder. The solder follows up around the joints between the ceramic and metal parts and quickly wets those parts which have been painted with titanium hydride. This method of sealing does not form a part of our present invention but is described and claimed in copending Beggs application, Serial No.

464,077, filed October 22, 1954, entitled Metallic Bond and assigned to the same assignee as this invention.

While we have shown and described a particular embodiment of our invention, it will be apparent to those skilled in the art that modifications may be made without departing from our invention and we, therefore, aim by the appended claims to cover any such modifications as wall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electric discharge device comprising three insulating rings arranged in a stack, a pair of ring-shaped metal terminals each interposed between adjacent ends of two of said insulating rings, a pair of end terminal members closing opposite ends of said stack, a cylindrical array of anode segments supported from said ring-shaped terminals within said insulating rings with alternate segments connected to one of said annular terminalsand the remaining segments connected with the other of said annular terminals, a conductive support extending inwardly from each of said end terminals-and terminating in spaced relation and a spiral cathode surrounding at opposite ends thereof said conductive supports.

2. The discharge device of claim 1 wherein the space between the ends of said supports lies at least partially beyond said array of anode segments in an axial direction.

3. An electric discharge device comprising three insulating cylinders arranged in a stack, a pair of annular metal terminals each interposed between adjacent ends of two of said cylinders, a pair of end terminal members closing opposite ends of said stack, a cylindrical array of anode segments supported from said annular terminals within said insulators with alternate segments connected to one of said annular terminals and the remaining segments connected with the other of said annular terminals, a conducting support extending inwardly from each of said end terminals and terminating in spaced relation and a spiral cathode supported at opposite ends thereof from said conducting supports.

4. An electric discharge device comprising three insulating cylinders arranged in a stack, a pair of annular metal terminals each interposed between adjacent ends of two of said cylinders, a pair of disc-shaped end terminal members closing opposite ends of said stack, a circular array of anode segments supported from said annular terminals within said cylinders with alternate segments connected to one of said annular terminals and the remaining segments connectedwith the other of said annular terminals, an integral cylindrical support extending inwardly fromv each of said end terminals and terminating in spaced relation and a spiral cathode surrounding at opposite ends thereof said cylindrical supports.

5. An electric discharge device comprising three insuiatiug cylinders arranged in a stack, a pair of annular metal terminals each interposed between adjacent ends of two of said cylinders, a pair of end terminal members closing opposite ends of said stack, an array of elongated anode segments supported in mutually spaced relation from said annular terminals within said insulators with alternate segments connected to one of said annular terminals and the remaining segments connected with the other of said annular terminals, a cylindrical support extending inwardly from each of said end terminals and terminating in spaced relation and a spiral cathode surrounding at opposite ends thereof said cylindrical supports.

6. A magnetron device comprising a cylindrical envelope, a cylindrical array of anode segments supported within said envelope, a pair of disc-like metal terminal members closing opposite ends of said envelope, an integral post extending axially inwardly from each of said terminals and terminating in spaced relation, a spiral cathode supported at opposite ends thereof the spaced ends of said posts, the spacing between said posts lying at least partially within said cylindrical array of anode segments whereby one of said posts extends within said array and forms a part of the cathode electrode.

7. A magnetron device comprising a cylindrical envelope, a cylindrical array of anode segments supported within said envelope, a pair of disc-like terminal members closing opposite ends of said envelope, a cylindrical post extending axially inwardly from each of said terminals and terminating in spaced relation, a spiral cathode surrounding at opposite ends thereof the spaced ends of said posts, the spacing between said posts lying at least partially within said cylindrical array of anode segments whereby one of said posts extends within said array and forms a part of the cathode electrode.

8. The magnetron device of claim 7 wherein said one post has a diameter equal to the outer diameter of said spiral except for the surrounded end portion thereof which is substantially equal in diameter to the inner diameter of said spiral.

9. A. magnetron device comprising a cylindrical envelope, a plurality of elongated anode segments supported within said envelope in a cylindrical array, a pair of cathode terminal members supported in insulated relation on opposite sides of said cylindrical array, a cylindrical post extending axially inwardly from each of said terminals and terminating in spaced relation, a spiral cathode surrounding at opposite ends thereof the spaced ends of said posts, the spacing between the ends of said posts being substantially less than the axial length of said 6 segments whereby one of said posts extends within said array and forms a part of the cathode electrode.

10. The magnetron device of claim 9 wherein said one post has a diameter equal to the outer diameter of said 5 spiral except for the surrounded end portion thereof.

No references cited. 

